Fusion plates are used to immobilize and fuse adjacent spinal vertebrae following a discectomy (spinal disc removal) or for immobilizing the area surrounding a corpectomy (removal of an entire vertebral body). Examples of fusion plates presently existing in the art are those produced by Medtronic Inc., Dupuy AcroMed, Inc., and Globus Medical, Inc., to name a few.
Discectomy and corpectomy procedures create a gap in the spine from the removed disc or vertebral body. Typically the gap is closed by inserting a bone graft or bone graft substitute. The adjacent vertebrae surrounding the discectomy or corpectomy site are then immobilized by attaching a fusion plate, usually on the anterior side of the spine, so that the vertebrae fuse to the bone graft, forming an entire fused section of the spine. Fusing the vertebrae to the bone graft requires that the vertebrae remain immobile.
Presently, in performing a discectomy or corpectomy, a distractor is used to spread the adjacent vertebrae so that the disc or vertebral body of interest can be removed. In use, a pair of distractor pins, which are essentially screws having a head for engaging with the distractor, are screwed into the vertebrae adjacent to the discectomy or corpectomy site. One pin is placed in the upper vertebra, and a second pin is placed in the lower vertebra, both vertebrae being directly adjacent to the discectomy or corpectomy site. The distractor is then coupled to the pins on the upper and lower vertebrae, above and below the site, and the vertebrae are then mechanically spread apart, for aiding in the removal of any remaining portion of the deteriorated disc or vertebral body, and also to create a gap for placing a bone graft.
Once the bone graft is placed, the distractor is removed. The distractor pins are then removed from the spine and a fusion plate is placed in a position keeping the adjacent upper and lower vertebrae as well as the bone graft immobilized. The plate is screwed into the upper and lower vertebrae.
Cervical fixation devices are commonly used to stabilize the cervical spine and promote successful bony fusion. Cervical fixation devices, including plate/screw devices, have been described for both the anterior and posterior application to the cervical spine. In spite of this, however, the available cervical plating systems have certain features that limit their usefulness in cervical spine reconstructive surgery. First, application of the available cervical plates requires a number of complex steps during surgery. Often, due to cumbersome instrumentation, application of a cervical plate may necessitate unnecessary steps to correctly size and apply the plate to the spine. Second, cervical plating systems often prevent accurate visualization of the bone graft/vertebra junction thus obscuring accurate placement of the cervical plate. Third, cervical plating systems often do not allow for compression of the bone graft, a step that is important in promoting bony fusion. Fourth, cervical plating systems generally use a cumbersome mechanism with several steps to prevent back out of the screws from the plate. Fifth, many cervical systems do not allow variability in placement of cervical screws and thus are not adaptable to anatomic variations in the cervical vertebra.
Moreover, current anterior cervical plating systems require the prior removal of the distractor pins placed in the vertebral bodies for distraction of the disc space during surgery and placement of the graft. This means that precise information about the localization of the vertebral bodies, their geometry and dimensions, which is garnered at the outset of the case during the placement of the pins, is lost. After the pins are removed at the end of the case, and frequently bone wax introduced to prevent bleeding from the pin sites, a plate is selected and introduced, typically by placing screws into the vertebral bodies above and below the fusion mass (graft). Error is introduced during this somewhat clumsy process, and the holes where the pins had been placed have to be avoided by the screws, for fear that entering the holes might not allow optimum securing of the screws.
Another problem associated with current anterior cervical plate systems is that placing the plate typically reduces the load across the fusion plane. However, it is known that bones fusion together better when there is a load applied across the fusion or fracture line.
U.S. Patent Application No. 2007/0123884 to Abdou describes different bone fixation systems which utilize distraction screws and fusion plates. Some of Abdou's proposed designs include a modular distraction screw, including a distal segment that can remain in the bone after a discectomy procedure and during plating. Abdou alleges that after a plate is lowered onto these distal segments, the head of these screws can be rotated to immobilize the plate. However, the design of these screws does not allow for true immobilization of the plate while it is being secured. Further, none of Abdou's proposed designs are able to provide compression (or distraction) along the axis of the fusion plate prior to securing the plate with bone screws.
Therefore, a need exists for a fusion plate system and method which allows a section of spine to be precisely compressed following a corpectomy or discectomy, so that sufficient and optimal immobilization and spinal fusion can occur.
There is a further need for a fusion plate system and method that allows a surgeon greater freedom to use both of his or her hands during placement of bone screws in a fusion plate.